Modulator with reactance element having nonlinearity

ABSTRACT

A reactance element in which a ferromagnetic, ferroelectric, or antiferroelectric material having point-symmetry, saturated nonlinearity is interposed as a modulation element between signal input terminals and output terminals and provided with excitation signal input terminals for receiving a carrier and is caused to operate as it is maintained at a constant temperature in the vicinity of its Curie point, a wave filter being inserted between the reactance element and the output terminals, whereby a DC input applied to the signal input terminals is modulated into an AC signal of the second harmonics of the carrier, which AC signal is equal in magnitude to the DC input and appears, at the output terminals after leaving the wave filter.

[72] Inventors Zenmon Abe;

Yoshio Furuhata; Yasuo Kato, all 01 Tokyoto, Japan [21] Appl. No. 633,497 v [22] Filed Apr. 25, 1967 [45] Patented Nov. 2, 11971 [73] Assignee Kabushiki Kaisha Hitachi Seisakusho Tokyo-to, Japan [32] Priority Apr. 27, 1966 [33] Japan [31] 41/263111 [54] MODULATOR WITH REACTANCE ELEMENT HAVING NONLINEARITY 5 Claims, 21 Drawing Figs.

[52] 11.8. C1 332/52, 332/30, 330/8 [51] lint. Cl 1103c 1/00 [50] Field of Search 330/7, 8; 331/36 C, 138, 139; 332/4, 30,51, 52; 340/174 [56] References Cited UNITED STATES PATENTS 2,152,016 3/1939 Baesecke et a1. 332/52 X Resistance-Capacity Oscillator" Radio, pages 16 and 18, Oct. 1945.

Primary Examiner-R0y Lake Assistant Examiner- Lawrence J. Dahl Attorney-Waters, Roditi, Schwartz 8: Nissen ABSTRACT: A reactance element in which a ferromagnetic, ferroelectric, or antiferroelectric material having point-symmetry, saturated nonlinearity is interposed as a modulation element between signal input terminals and output terminals and provided with excitation signal input terminals for receiving a carrier and is caused to operate as it is maintained at a constant temperature in the vicinity of its Curie point, a wave filter being inserted between the reactance element and the output terminals, whereby a DC input applied to the signal input terminals is modulated into an AC signal of the second harmonics of the carrier, which AC signal is equal in magnitude to the DC input and appears, at the output terminals after leaving the wave filter.

PATENTED NUVZ I971 SHEET 3 0F 3 64 FILTER MODULATOR Wll'llllll lltEAC'llANCE ELEMENT lfIAVlNG NONLJINEAMTY This invention relates to circuits in which elements having point-symmetry nonlinearity are used. More particularly, the invention concerns modulators and amplifiers in which ferromagnetic and ferroelectric materials are used for the abovestated elements.

As one general example of devices in which use is made of ferromagnetic or ferroelectric materials as elements having point-symmetry nonlinearity, modulators have heretofore been known. In a modulator of this type when the element is excited by a carrier such as a sine wave carrier, and, at the same time, DC or subaudiofrequency input signal is impressed, the operational point shifts to a region of nonlinearity in the characteristic curve of the element, and, as a result, even harmonics proportional to the input signal are included in the modulated wave. This result is utilized in these modulators.

Examples of modulators of this type are the even-harmonictype modulator in which even-harmonics are utilized, the amplitude-difference modulator in which the amplitude difference due to the polarity of the modulated wave produced by the shifting of the operational point or the proportional relationship to the input signal of the even-harmonics arising from the amplitude rim'erence is utilized, and the peak-height modulator in which utilization is made of the phenomenon whereby, in the case wherein the output waveforms of a differential modulator have some phase difference, shifting of the operational point causes the amplitudes of output waveforms of the same polarity to increase and the amplitudes of output waveforms of different polarity to decrease.

Furthermore, in accordance with the same thought, excitation of the aforementioned element may be accomplished with an amplitude modulated carrier instead of a sine wave carrier. In addition to these modulators, examples of known circuit devices in which point-symmetry nonlinearity is used are amplificrs such as dielectric amplifiers and magnetic amplifiers. These amplifiers are adapted to amplify input signals by exciting the aforementioned element, in each case, with a carrier having an amplitude of a magnitude corresponding to the re gion of steep rise in the characteristic curve of the element.

However, in the case of even-harmonic-type modulators known heretofore in which ferroelectric materials or ferromagnetic materials are used as reactance elements, the operational temperatures thereof are so set that the modulators operate at temperatures in the vicinity of ordinary room temperature, and temperatures near the Curie points of the elements are avoided. Consequently, these modulators have heretofore been unavoidably accompanied by the following drawbacks.

The case wherein a reactance element using a ferroelectric material is used as a modulation element will first be considered. Since a large spontaneous polarization exists in a ferroelectric material at a temperature near room temperature,

the electric field, that is, the coercive field, required for inverting this spontaneous polarization becomes large. Then, for an even-harmonic-type modulator to operate normally, it is necessary to apply a carrier of an amplitude which is substantially greater, for example, by two to three times, than that of the coercive field.

Accordingly, if the coercive field is large, the amplitude of the carrier for driving the above-mentioned element will also become unavoidably large as a natural result. Consequently, the extremely small amplitude of the input signal will become even smaller in comparison with the carrier amplitude, whereby discrimination of the signal thus modulated will become difficult, and a wave filter particularly with a steep cutoff characteristic will become necessary. Furthermore, during the inversion of the ferroelectric domains, Barkhausen noise proportional to the magnitude of the spontaneous polarization is produced. In addition, the existence of spontaneous polarization becomes a cause of the so-called memory effect, that is, the phenomenon whereby, even if this noise is removed by applying a particularly excessively large DC input signal, the output signal does not immediately return to its original value, and this effect becomes a cause of zero drift.

In the case where a reactance element employing a ferromagnetic material is used as the modulation element, the only difference is that a magnetic field is used instead of an electric field, and a spontaneous magnetization or magnetic domain exists. In this case also, drawbacks similar to those in the case where ferroelectrics are used still exist.

It is an object of the present invention to provide a new even-harmonic-type modulator, particularly a second-harmonic-type modulator, in which the modulation element is operated while being maintained at a constant temperature in the neighborhood of the Curie point in order to overcome the above-described drawbacks.

In order to achieve the above objects and other objects as set forth hereinafter, the present invention, briefly summarized, provides a modulating device characterized by the combination of a modulation element in which a nonlinear reactance element is used, means for exciting this modulation element with a carrier, means to apply to the input side of this element a DC input signal or an input signal of subaudiofrequency, means for leading out from the output side of this element a modulated output signal, and a heating device for radiofrequency heating this element to maintain it at a constant temperature in the neighborhood of the Curie point of the element.

In this modulating device, the modulation element is excited by the carrier, and, by the shifting of the operational point due to the input signal, an even-harmonic output signal which contains second-harmonics and is proportional to the magnitude of the input signal is obtained at the means for leading out a modulated output signal. As a net result, the input signal is converted into an alternating current signal.

Accordingly, a specific object of the invention is to provide an even-harmonic-type modulator capable of converting a DC or subaudiofrequency input signal from which Barkhausen noise and memory effect proportionall to the magnitude of the spontaneous polarization of the ferromagnetic material have been removed into an alternating output signal.

Another object of the invention is to provide an even-harmonic-type modulator in which compensation is provided for the electric field produced by the defects of ferroelectric crystals maintained at a constant temperature in the neighborhood of the Curie point of the element,

Still another object of the invention is to provide an evenharmonic-type modulator suitable for use as a solid-state, DC to AC converter having a very high input resistance and simple circuit composition and arrangement without vibrating parts.

A further object of the invention is to provide an even-harmonic-type modulator in which a ferromagnetic material maintained at a constant temperature in the neighborhood of the Curie point is used as the modulation element. That is, an object of the invention is to provide a magnetic modulator which is unaffected by effects such as Barkhausen noise due to irregular rotation of the magnetic domains of ferromagnetic materials.

A still further object of the invention is to provide a dielectric or magnetic amplifier in which a modulation element maintained at a constant temperature in the neighborhood of its Curie point is excited by an exciting signal having an amplitude of a magnitude corresponding to the region of steep rise of the nonlinear characteristic curve of the element.

An additional object of the invention is to provide a device for maintaining the above-mentioned modulation element at a constant temperature in the neighborhood of its Curie point.

The nature, principle, and details of the invention, as well as the utility thereof, will be more clearly apparent from the following detailed description when read in conjunction with the accompanying drawings, in which like parts are designated by like reference numerals.

In the drawings:

FIGS. 1(a), 1(b), 1(0), and 1(d) are graphical representations respectively indicating waveforms for an explanation of the principle and operation of the invention;

FIGS. 2(a) and 2(b) are graphical representations respectively indicating relationships between spontaneous polarization of ferroelectric materials to temperature;

FIG. 3 is a circuit diagram indicating the composition and arrangement of one example of embodiment of the invention;

FIGS. 4(a) and 4(b) are graphical representations indicating relationships between dielectric fiux density to electric field (E-D characteristics) of ferroelectric materials;

FIGS. 5(a) and 5(bare circuit diagrams indicating the composition and arrangement of another embodiment of the invention;

FIGS. 6(a) and 6(b) are schematic diagrams, partly in section, respectively showing examples of construction of capacitors used in the modulating device according to the invention;

FIG. 7(a) is block diagram indicating the composition and arrangement of an oscillator constituting an embodiment of the invention for maintaining constant temperature in the neighborhood of the Curie point of a modulation element;

FIG. 7(b) is a planar view showing an example of a heated capacitor for use in the oscillator shown in FIG. 7(a);

FIG. 8 is a circuit diagram showing a specific example of circuit arrangement of the oscillator shown in FIG. 7 (a); and

FIGS. 9, 10(a), l0(b), and 11 are circuit diagrams showing examples of embodiment of the invention.

The principle of the present invention will first be described in detail with reference to the diagrams of waveforms in FIGS. 1(a) through 1(d) and with respect to the case wherein a capacitor in which a ferroelectric material is used is utilized as a modulation element.

When a voltage of sine wave waveform as indicated in FIG. l(b) is applied as a carrier from the outside to a capacitor in which there is used a ferroelectric material having a pointsymmetry nonlinearity in the relationship between electric field E and dielectric flux density D as indicated in FIG. 1(a), the current flowing to the outside assumes a waveform as indicated in FIG. 1(0) and does not contain even-harmonic components.

Then, when a very small direct current or subaudiofrequency voltage is superposed as an input signal on the above-mentiqned capacitor, the operational point deviates from pointsymmetrical center, and the above-mentioned current to the outside assumes a waveform as indicated by dotted line in FIG. 1(c). This means that even-harmonics have been added to the current waveform, which now contains many secondharmonics of the carrier voltage as indicated in FIG. 1(d). Furthermore, in the case where the above-mentioned DC or subaudiofrequency input signal is very small, the second-harmonies are proportional to the input signal, which means that the in small input signal has been converted into an AC signal.

While the above principle has been described with respect to a second-harmonic-type modulator, the same principle can also be applied in the following manner to provide an amplifier. A bias voltage is applied particularly beforehand to the capacitor, and the input signal is superposed thereon. Excitation is efi'ected by a carrier having an amplitude of a magnitude corresponding to the region of steep rise of the nonlinear characteristic curve as indicated in FIG. 1(a), whereu pon the capacitance of the capacitor varies with the input signal similarly as in the case of a modulator, and the carrier current in accordance with this capacitance variation is caused to increase and decrease. A device for accomplishing this operation is called a dielectric amplifier.

In the case, also, wherein a ferromagnetic material is used, the same principle as in a modulator or amplifier in which a ferroelectric material is used is valid, the only difference being that the characteristic curve of dielectric flux density with respect to electric field as shown in FIG. 1(a) becomes a characteristic curve of point-symmetry nonlinearity of magnetic flux density (or magnetic induction") with respect to magnetic field.

The above-described principle is utilized in the devices of the present invention, the aforementioned reactance element being caused to operate as it is maintained at a constant temperature in the neighborhood of its Curie point. As one example of embodiment of the invention, the case wherein a reactance element in which a ferroelectric material is used, is utilized as a modulation element will now be described below.

In general, the aforementioned spontaneous polarization has a characteristic such that its magnitude Ps decreases gradually with temperature and becomes zero at the Curie point To in the case of second-order transition as indicated in FIG. 2(a), but in the case of first-order transition as indicated in FIG.2(b), this magnitude Ps varies discontinuously and drops abruptly to zero at the Curie point To. Consequently, in the case of first-order transition, noise is produced by this discontinuous characteristic. Where low noise is not required, however, this noise does not present a problem for practical purposes. Furthermore, there are some materials in which the nonlinearity of the aforementioned E-D characteristic is greater than that in second-order transition, and, inversely, the DC to AC conversion efficiency becomes high.

In the case of second-order transition, however, since the magnitude Ps of spontaneous polarization varies continuously to zero, noise due to discontinuity as in first-order transition is not produced. Since the Barkhausen noise arising with the inversion. of the ferroelectric domains is proportional to the spontaneous polarization, it decreases abruptly in the neighborhood of the Curie point To and becomes zero at the Curie point and higher temperatures.

On one hand, the aforementioned coercive field is of the following character. According to the Devonshire theory, in the case where there is no ferroelectric domain, the magnitude Ec of the coercive field may be represented as a function of temperature by the following equation (I).

Er=0.272 A 13 (To-T) (l) The case of triglycine sulfate used as a ferroelectric material will now be considered as an example. The magnitude Ec of the coercive field in this case may be expressed by the following equation (2) Ec'=l.67 K (To-T) (c.g.s. units) =5 00 K To-T) volt/cm., (2) where K is a correction coefficient depending on the mechanism of creation and growth of the domains which is to become dominant in an actual domain inversion.

In the case of a capacitor constituting a reactance element in which triglycine sulfate is used as a ferroelectric material, a carrier amplitude which is approximately two times that of the coercive field is necessary for normal operation. Furthermore, if the thickness of the triglycine sulfate is selected to be 0.1 mm., the magnitude of the amplitude Vc of the carrier in terms of the required RMS voltage (effective voltage) can be derived from the above equation 2) and expressed by the following equation. Vc=7.07 K (T-To) volt (3) Then, with respect to a DC input signal of very low value of 10 millivolts or less, if the actual attenuation of the carrier due to a band-pass filter is assumed to be 60 db. with respect to the aforementioned second-harmonics, and the efficiency of conversion from the DC input signal into a second-harmonic AC output signal is assumed to be 50 percent, the carrier amplitude must be 5 volts or less.

In the case of triglycine sulfate, furthermore, since the correction coefficient may be K I with a carrier frequency of 50 kc./sec., the deviation allowable from the Curie point isexpressed by the following equation (4).

To-T O. 8 C. (4)

Accordingly, use of this triglycine sulfate is possible up to a temperature approximately 1 C. lower than the Curie point.

On the other hand, with respect to the aforementioned memory effect, temperatures up to approximately 1 below the Curie point do not pose much of problem. That is, temperatures which can be used in actual practice are in the neighborhood of the Curie point. Furthermore, if the operational temperature of the ferroelectric material were to exceed to the Curie point, the spontaneous polarization of the ferroelectric material would disappear, whereby the aforementioned coercive field would cease to exist. Therefore, aforementioned carrier amplitude applied to the element become smaller in comparison with the carrier amplitude in the case when the element is at a temperature below the Curie point thereof, and both of the aforementioned memory effect and the Barkhausen noise are eliminated. Consequently, the operation of the modulator according to the present invention is remarkably improved.

The above description concerning ferroelectric materials is analogously applicable also to the case of ferromagnetic materials. For example, since the Barkhausen noise generated with the inversion of the magnetic domains is proportional to the spontaneous magnetization of a ferromagnetic material, the spontaneous magnetization decreases abruptly at temperatures in the neighborhood of the Curie point and is almost completely nonexistent at the Curie point and higher temperatures.

The above-described principle is utilized in the present invention, one embodiment of which is illustrated in FIG. 3 in the form of a modulator. As a modulation element for converting an input into alternating current in this modulator, there is provided a capacitor ll in which triglycine sulfate is used as a ferroelectric material, and which is maintained at a constant temperature in the neighborhood of the Curie point of the triglycine sulfate. One of the electrodes of this capacitor ii is connected to earth (ground).

A DC signal or a subaudiofrequency signal to be converted into alternating current is introduced through input terminals 2 and 3S and, passing through a high resistance t, is applied to the capacitor I. Input terminals 5 and 6 are provided for the introduction of a carrier for exciting the capacitor 1, this carrier being applied to the capacitor 1 by way of a transformer 7. A band-pass filter t is connected to the capacitor l and accomplishes seiection of an AC signal arriving from the capacitor ll and having a frequency which is two times that of the carrier, the AC signal thus selected appearing at output terminals 5 and ll llb.

The filter h may be an ordinary filter of the type consisting essentially of capacitors and resistors, or it may be A resonance circuit which tunes its output frequency to two times the carrier frequency.

The carrier input side and the output side of the AC output signal are respectively provided with blocking capacitors l1 and 12. In this circuit, the blocking capacitor I2 and the bandpass filter fi form an output section I13, and the transformer 7 and the blocking capacitor form an excitation section M for exciting the capacitor l.

The circuit of the above-described composition and arrangement according to the invention operates in the following manner.

The DC or subaudiofrequency input signal is introduced through the input terminals 2 and 3 and applied by way of the high resistance 4 to the capacitor II and superposed on the carrier signal applied to the terminals 5 and 6, whereby a signal of the resultant superposed waveform is applied to the capacitor 1. As a result, in accordance with the above-described principle, an output signal of point asymmetrical waveform containing second-harmonics is obtained in the output section 13.

This output signal is passed through the band-pass filter 8 where the carrier is removed, and only an AC output of second harmonics of a magnitude which is proportional to the input signal is selected and appears at the output terminals 9 and 110. As a result, it is possible to obtain an AC output signal which is proportional to the magnitude of a DC input signal. Furthermore, if necessary, this AC signal thus obtained may be amplified with an amplifier. Indeed, the present invention is not limited to obtain only second-harmonics, but may be used to selectively obtain, if necessary, further high-order even-harmonies by using an appropriate filter or resonance circuit which is tuned with the desired even-harmonics.

While the above description relates to the specific case wherein a single capacitor is used as a modulation element, they present invention is not limited to only this case, being applicable also to the case wherein, even when the capacitor is maintained at a constant temperature equal to or higher than the Curie point, a slight electric field remains because of crystal defects in the ferroelectric material used.

When such an electric field remains, the dielectric flux density D versus electric field IE characteristic becomes equivalent to that when a DC input signal is applied, even when there is no DC input signal, and, in comparison with the theoretical point-symmetrical characteristic as indicated in FIG. 4(a), generates a second-harmonic voltage proportional to the remaining electric field, thereby assuming an offset configuration as indicated in FIG. 41(1)).

One example of the invention which may be applied for reducing this offset state occurring in such a case is illustrated in FIG. 5(a). By combining two capacitors l5 and to respectively having remaining electric fields of the same magnitude, these remaining electric fields can be neutralized and compensated. The capacitors and 116, which are formed by identical ferroelectric crystals, are maintained at a constant temperature in the neighborhood of the (Curie point and are used as modulation elements for converting the input into alternating current.

One electrode of the capacitor 115 is connected at a junction 211 to one electrode of the capacitor 16. The other electrodes of the capacitors l5 and 16 are respectively connected to terminals 20 and 19 of the secondary winding 17 of a transformer 18. The middle point of the secondary winding 117 is con nected to earth (ground). Thus, the secondary winding 17 and the capacitors l5 and 116 form a bridge circuit. The other parts of the circuit are similar to corresponding parts in the circuit shown in FIG. 3 and are designated by the same reference numerals as in FIG. 3. Further, in the present invention, it may also be possible to substitute impedance elements 17 and 17 for the transformer l8, these impedance elements and the capacitors l5 and 16 forming a bridge circuit, as indicated in FIG. 5(b).

In the operation of the above-described circuit, a DC or subaudiofrequency input signal is introduced into the circuit through input terminals 2 and 3 and, by way of the high re sistance d, charges the capacitors l5 and 116, while a carrier is applied through terminals 5 and 6 and the transformer 18 to the capacitors 115 an 16, whereby, by the aforedescribed principle, an AC output signal consisting almost entirely of second harmonics of the carrier is generated in the output section 13.

More specifically, since the bridge circuit made up of the capacitors l5 and 16 and the secondary winding 117 is maintained steadily in balance or equilibrium, the carrier does not appear in the output section 13, and only the above-mentioned second-harmonics appear. When the bridge circuit is not sufficiently in balance, a band-pass filter h as indicated by dotted line in FIG. 5(a) may be used. Moreover, the filter d may be of simple type.

In order to attain good bridge balance, there must be good coincidence of the characteristics of the two capacitors in which ferroelectric materials are used. For example, a characteristic of these capacitors is that their capacitances vary abruptly with variation in temperature in the vicinity of the Curie point. Furthermore, the losses in these capacitors are greatly influenced by slight differences in the composition of the ferroelectric material and by very small variations in the production conditions.

In addition, since an ofiset occurs in the characteristic of a capacitor as described above when a remaining electric field exists, a possible measure is to cause the magnitudes of the remaining electric fields in two capacitors to coincide and to connect the two capacitors in a manner whereby these electric fields nullify each other. In such a case, the various requirements described above can be effectively fulfilled at one time by forming the two capacitors as a pair with the same sheet of ferroelectric crystal of uniform thickness and making their electrode areas equal.

One effective method of preparing a ferroelectric material of uniform thickness is to utilize the cleavability possessed by the crystal. For example, a ferroelectric material such as triglycine sulfate is a crystal having cleavability in a plane perpendicular to the [010] axis exhibiting ferroelectric effect. The two surfaces of a crystal of this type 'after cleavage are very smooth and flat, and are parallel with high precision. Accordingly, by forming two pairs of electrodes of equal area by evaporation deposition on these surfaces, electrodes of excellent and equal electrical characteristics can be obtained.

By this method, the production conditions under which the ferroelectric materials of the two capacitors are fabricated become exactly the same, and, furthermore, even the temperature characteristics of the two materials are caused to be closely alike. Therefore, the nonlinear, electric field E versus dielectric flux density characteristics of the two capacitors are coincidentally matched not only with respect to temperature but also with respect to capacitance and losses. Furthermore, when these two capacitors are closely positioned, the magnitudes and even the directions of the aforementioned remaining electric fields exhibit a close interrelationship, whereby it is possible, by appropriately connecting the two capacitors, to compensate for the offset characteristics arising, from the remaining electric fields. Thus, on the basis of the above considerations, it is possible to obtain a high degree of bridge balance by fonning a pair of capacitors with the same ferroelectric material and inserting these capacitors respectively into two arms of the aforedescribed bridge circuit.

A pair of capacitors fabricated as described above are connected in the following manner in accordance with the invention. FIG. 6(a) shows, in section, one example of two capacitors fabricated on the same ferroelectric crystal 22 in the above-described manner and indicates the manner in which the electrodes are connected. Two electrodes 23, 23 formed on one surface of the common ferroelectric crystal 22 are commonly connected by a conductor to a single common terminal 25. The two electrodes 23a,23a, formed on the opposite side of the ferroelectric crystal 22 are provided respectively with terminals 26 and 27. These terminals 25, 26, and 27 are connected respectively to the junction 21 and terminals 20 and 19 in the circuit shown in FIG. 5. By this connection arrangement, it is possible to attain good balancing of the bridge. Furthermore, by leading out the common terminal 25 from the same electrode formed on the same surface of the ferroelectric material 22, it is possible to effect an economy in the length of the conductor.

FIG. 6(b) shows, in section, two capacitors positioned on the same ferroelectric material 28 and indicates an improved manner of connection. Electrodes 29, 29 and electrodes 29a, 290 are respectively formed on opposite sides of the ferroelectric material 28. The electrode 29 of one capacitor is connected with the electrode 290 of the other capacitor to a common terminal 31. The other electrodes 29a are connected respectively to terminals 32 and 33. The terminals 31, 32, and 33 are connected respectively to junction 21 and terminals 20 and 19 in the circuit shown in FIG. 5.

When two capacitors are formed in close proximity by electrode of equal area on a ferroelectric structure of uniform thickness as described above, the remaining electric fields of the ferroelectric material corresponding to these capacitors at the Curie point or higher temperature due to crystal defects exhibit a close interrelationship. Then, when one electrode of one capacitor on one surface of the ferroelectric structure is connected commonly with the electrode of the other capacitors on the opposite surface, the directions of the two capacitors equivalently become antiparallel. For this reason, the remaining electric fields of the ferroelectric structure nullify each other, whereby the above-described construction and connection are effective in reducing the aforedescribed offsetting of the characteristic curve.

In addition, it is possible to increase the effect of mutual nullification and compensation of the remaining electric fields by variously changing the shapes of the electrodes, for example, by making electrodes of comblike shape and disposing the electrodes of each pair in intermeshed, labyrinthine arrangement.

For maintaining capacitors constituting a reactance element which are fabricated with a ferroelectric material and used as a modulation element in the manner described above at a constant temperature in the neighborhood of the Curie point of the ferroelectric material, any conventional constant-temperature vessel may be utilized. However, in the present invention, for maintaining said element at a constant temperature, a novel radiofrequency dielectric heating device is provided, as indicated in FIG. 7(a), which comprises, a bridge circuit 35 having arms consisting of a heated capacitor 34, coils 83, 84, and capacitors and constituting a feedback circuit and a high-frequency power amplifier constituting an amplifier 36.

In the circuit of this oscillator, the heated capacitor 34 has an electrode construction and arrangement as illustrated by the planar view of FIG. 7(b) and the sectional view of FIG. 7 (c). This capacitor 34 comprises a ferroelectric crystal structure 37 and a pair of annular electrodes 38, 38' formed on both sides of ferroelectric crystal 37 to oppose each other. These are also provided two pairs of electrodes 39, 39' formed on both sides of the crystal 37 and surrounded by the annular electrodes 38, 38' in close proximity on the ferroelectric crystal 37, the electrode 38 being of annular shape and surrounding the electrodes 39, 39 in close proximity thereto. The electrodes 39, 39 thus form two capacitors, which are connected as indicated in FIG. 6 and used as the modulation element in a circuit arrangement as illustrated in FIG. 5. The capacitor formed by the electrode 38 is the heated capacitor.

The high-frequency output of the above-mentioned oscillator is applied to the electrode 38, which is thereby heated by dielectric heating. As the same time, this heating results in a heating with uniform temperature distribution of also the capacitors formed by the electrodes 39, 39 since the same ferroelectric crystal structure 37 is used in these capacitors. The

, resulting effect on these capacitors is the same as though they were subjected to dielectric heating.

Furthermore, it is possible, of course, by forming a single electrode 39 on the ferroelectric crystal 37 to form one capacitor, to use this capacitor as the modulation element in a circuit arrangement as illustrated in FIG. 3.

The principle of operation of the capacitors maintained at a constant temperature in the neighborhood of the Curie point will now be considered. When the temperature of the capacitor formed by the electrode 38 arises as a result of highfrequency heating, the capacitance of the capacitor varies rapidly in accordance with the Curie-Weiss law. This capacitance variation is accompanied by a variation in the return ratio [3 of the bridge circuit 35.

If the temperature rise due to heating is excessive, the capacitance will vary to cause a decrease in the return ratio, and the output of oscillation will thereby decrease, or, in an extreme case, the balance point of the bridge will be exceeded, whereby an inversion of the phase shift will occur to cause the oscillation to stop. On the other hand, if the temperature drops, the return ratio will increase, whereby the output of oscillation will increase to increase the heating rate.

That is, the capacitance, i.e., the temperature, of the heated capacitor 34 is so controlled that the oscillation condition expressed by AB=1, where a is the gain of the amplifier circuit 36, is satisfied, and this temperature is constantly maintained in the neighborhood of the Curie point. By this control, the temperature of the two capacitors formed by the electrodes 39, 39 and used as a modulation element is set at a desired constant temperature value in the neighborhood of the Curie point as a result of the dielectric heating of the capacitor formed by the electrode 38.

Effective measures particularly for reducing as much as possible the heat transmission to the surroundings are to use a conductor which is as thin and long as practicable from the electrodes and to seal the entire element in a vacuum vessel. Furthermore, while an additionally provided heated capacitor is used in the above-described example, it is also possible in accordance with the present iniEntion to heat the capacitors used as the modulation element, themselves, and thereby to obtain the same operation.

A specific example of a circuit for the above-mentioned oscillator for accomplishing heating in the above-described manner is illustrated in lFIG. 3. This circuit is made up of a bridge circuit 33 and an amplifier 36. The bridge circuit '33 has in one arm thereof a heated capacitor Ail including capacitors used as the modulation element and constructed as shown in FIG. 7(h) and in the other three arms a capacitor 411 and two parts of a winding d2 having a middle neutral tap connected to earth (ground) and constituting the secondary winding of a transformer 33.

The amplifier 36 is an ordinary two-stage amplifier in which transistors 441 and A3 constitute the principal components. This amplifier is further provided with bias resistors 46, 47, and 43 connected to the base electrode of the transistor 44, a bias resistor t9 connected to the collector electrode of the transistor M, bias resistors 30 and 31 connected to the base electrode of the transistor A3, a bias resistor 32 and a bypass capacitor 33 connected to the emitter electrode of the transistor A3, a coupling capacitor 33 connected between the bridge circuit 33 and the base electrode of the transistor 44, a coupling capacitor 33 connected between the collector electrade of the transistor M and the base electrode of the transistor A3, and power source terminals 37 and 33.

The output of the amplifier 36 of the above-described organization is applied from the collector electrode of the transistor d3, through the transistor 43, to the bridge circuit 33. Positive feedback is transmitted from the junction between the heated capacitor 40 of the bridge circuit 35 and the capacitor ill, through the coupling capacitor 1, to the base electrode of the transistor M of the amplifier 36.

Thus, the bridge circuit 33 and the amplifier 36, in combination, constitute the aforementioned oscillator. By the operation of this oscillator, the capacitors contained in the heated capacitor Ail and used as the modulation element operate as they are maintained at a constant temperature in the neighborhood of the Curie point.

Because of the above-described composition and arrangement, and particularly since the modulation element is maintained at a constant temperature in the neighborhood of its Curie point, the second-harmonic-type modulator according to the invention, differing from known modulators accomplishing inadequate DC to AC conversation, has the following advantageous features.

In this modulator of the invention, it is possible to eliminate or greatly decrease the lBarkhausen noise, which is proportional to the magnitude of the spontaneous polarization of the ferroelectric material, and the memory effect. At the same time, it is possible to reduce also' the offset voltage due to remaining electric fields caused by crystal defects of the ferroelectric material.

Furthermore, in comparison with those of known DC to AC converters such as mechanical shoppers, the input resistance of the modulator of the invention is extremely high, being ohms or higher. Another advantage of the modulator of the invention is that, since it does not have vibrating parts and is in a solid state, it has excellent resistance to vibration, and its circuit composition and arrangement becomes simple. Accordingly, there is afforded the possibility of miniaturization and reduction of weight of the entire device, reduction of power consumption, lowering of price, and lengthening of serviceable life of the device.

While the above description relates to a second-harmonictype modulator in which a ferroelectric material is used as the modulation element, the present invention is not limited thereto, being applicable with equal facility and effectiveness also to other devices as, for example, second-harmonic-type modulators of the type in which a ferrite is used as the modulation element.

One example of such application is illustrated in FIG. 9, which shows the organization of a magnetic modulator. The

lllll principal parts of this magrEtiFm-odulator are an excitation section 114, an input section, and an output section 113 all coupled by a ferrite core 39. The excitation section It comprises a carrier oscillator 63, an input resistor 67, and a primary coil for excitation wound around the core 39 and connected by way of the resistor 67 to the oscillator 63. The input section comprises input terminals 63 for introducing a DC or subaudiofrequency input signal and a coil 6i wound around the core 39 and connected to the input terminals 63. The output section comprises a secondary coil 62 for output wound around the core 39, a band-pass filter 64 connected to the secondary coil 62, and output terminals for leading out an AC output signal from the filter GA.

The magnetic modulator of the above-described organization operates in the following manner. A DC or subaudiofrequency signal is applied to the input terminals 63 of the coil 61, which is thereby excited, and the core 39 is excited by the carrier oscillator 63 and the primary coil 60 connected to the oscillator 63. Then, in accordance with the aforedescribed principle, even harmonics containing a large number of second harmonics are derived from the output secondary coil 62 and, passing through the band-pass filter 63, are free from the carrier. As a resultant effect, only an AC output of secondharmonics of a magnitude proportional to the above-mentioned input signal appears at the output terminals 66. That is, an AC output signal proportional to the magnitude of the DC or subaudiofrequency input signal can be obtained.

During this operation, the core 39 used as the modulation element is subjected to induction heating by an oscillator in which the aforedescribed principle is utilized, and its tempera ture is thereby maintained at a constant value in the neighborhood of the Curie point.

More specifically, instead of the heated capacitor constructed to contain the capacitors used as the modulation element and fabricated with a ferroelectric material in the bridge circuit 35 constituting the feedback circuit shown in FIG. 7(a), a heated coil is wound around the core 39 and incorporated as one arm of a bridge circuit, and the other three arms are made up of an ordinary capacitor and coil to form a bridge. By the use of the bridge thus formed, the same operational effect as in the case where a heated capacitor is used as described above can be attained, whereby the temperature of the core 39 can be maintained at a constant value in the neighborhood of the Curie point.

In a conventional modulator, when it is used for measurement particularly of external magnetic fields of very low magnitude, the limit of this measurement is essentially determined by the Barlrhasen noise. In contrast, in the modulator according to the present invention of the above-described organiza tion, particularly since the modulation element is operated at a constant temperature in the vicinity of the Curie point, there is no generation of the Barkhausen noise due to irregular orientation of the magnetic domains of the ferromagnetic material. Therefore, measurement of extremely low-magnitude magnetic fields becomes possible, the lower limit of measurement being remarkably lowered.

For detecting external magnetic fields by means of the magnetic modulator illustrated in FIG. 9, the magnetic flux generated by these external magnetic fields in the core 39 may be used as the input signals without using the input signal coil 61..

While the foregoing description relates the application of the present invention to second-harmonic-type modulators in each of which use is made of modulation element wherein a ferroelectric material or ferromagnetic material is utilized as a reactance element, the present invention is not limited to modulators, being applicable also to amplifiers in accordance with the principle described hereinbefore.

In one example of such application to amplifiers as illustrated in FIG. lll(a), the invention is applied to a dielectric amplifier. Two capacitors 63, 63 formed by the use of one and the same ferroelectric material is used as a modulation element and connected in series with a carrier oscillator 69, to

which a load 70 is connected in series. The load 70 includes a rectifier circuit 77 made up of diodes 75 and a load resistance 76 as shown in FIG. (b).

One electrode of each of the capacitors 68, 68 is connected to a common tenninal 72 of two input terminals 72, 72, the other input terminal 72 being connected by way of an input resistance 74, a DC bias source 71, and high-frequency choke coils 73, 73 in parallel connection to the other electrodes of the capacitors 68, 68. The input terminals 72, 72 are for introducing an input signal to be superposed with bias voltage supplied by the bias source 71.

In the above-described circuit, the two capacitors 68, 68 are constructed as shown in FIG. 7(b) by the use of the same ferroelectric material and are heated by dielectric heating as described hereinbefore by an oscillator consisting of a feedback circuit 35 and an amplifier 36 as illustrated in F IG. 7(a). Thus, the capacitors 68, 68 operate as the modulation element as they are maintained at a constant temperature in the vicinity of the Curie point.

In the operation of the dielectric amplifier as described above, the carrier oscillator 69 applies to the capacitors 68, 68 a voltage having an amplitude of a magnitude corresponding to that within the region of steep rise of the nonlinear characteristic curve of the ferroelectric material of the capacitors, while, on one hand, a subaudiofrequency input signal is introduced through the input terminals 72 and, in superposed state with a bias voltage from the bias source 71, is applied to the capacitors 68, 68.

As a result, in accordance with the aforedescribed operational principle, the carrier current varies with the variation in the capacitances of the capacitors 68, 68, and an AC output of a frequency equal to that of the carrier is rectified in passing through the rectifier 77, the resulting output appearing at the load resistance 76. Thus, as a total result, the above-mentioned input signal is amplified.

Another embodiment of the invention as applied to a magnetic amplifier is illustrated in FIG. 11. In this circuit, there are provided two cores 81 and 82, around which two output windings 78, 78 are respectively wound and connected in series to a carrier oscillator 69 and a load 70. Operation windings 79, 79 to which a DC or subaudiofrequency input signal is applied through input terminals 80 are also wound respectively around the cores 8] and 82. The cores 81 and 82 are maintained by induction heating as described hereinbefore at a constant temperature in the vicinity of their Curie point. The load 70 includes a rectifier 77 and a load resistance 76 as shown in FIG. 10(b).

In the operation of the magnetic amplifier of the abovedescribed organization, the cores 81 and 82 are excited by a carrier signal from the carrier oscillator 69, while a DC 0 subaudiofrequency input signal is introduced through the input terminals 80 and applied to the operation windings 79. Then, on the basis of the aforedescribed principle, the carrier current is caused to vary in accordance with the magnetic flux variation due to the input signal and becomes an AC output signal, which, upon passing through the rectifier 77, appears as a rectified signal of average value at the load resistance 76. As a total result, the input signal is amplified.

Because of the above-described organization, and since the modulation element is maintained at a constant temperature in the vicinity of its Curie point, the amplifier according to the invention, differing from known dielectric or magnetic amplifiers, has excellent temperature characteristics, has no hysteresis effect, and has good time response.

While the foregoing disclosure covers the use of only ferroelectric and ferromagnetic materials as reactance elements, it is also possible to se antiferroelectric materials as reactance elements since they exhibit the same characteristics as ferroelectric materials at temperatures in the vicinity of their Curie points.

Accordingly, it should be understood that the foregoing disclosure relates to only preferred embodiments of the invention and that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purposes of the disclosure, which do not constitute departures from the spirit and scope of the invention.

What we claim is:

l. A signal modulating device comprising: at least one nonlinear reactance element which exhibits nonlinear reactance characteristics in accordance with a change in a signal applied thereto at a constant temperature in the vicinity of the Curie point thereof; heating means for maintaining said nonlinear element at the constant temperature in the vicinity of the Curie point during operation; means for applying to said nonliner reactance element a carrier having a relatively high alternating frequency with respect to said input signal; input means including an input impedance element for applying an input signal to said nonlinear element through said input impedance element said input impedance element being designed to exhibit a relatively low impedance in response to said input signal, but a relatively high impedance in response to said carrier; and output means for selectively obtaining from an output signal of the nonlinear reactance element even-harmonics of the carrier modulated by said input signal.

2. A signal modulating device as defined in clam 1, wherein said nonlinear reactance element is a dielectric capacitor utilizing dielectric material which exhibits nonlinear characteristics of its dielectric constant in accordance with change in a signal applied thereto, and said heating means comprises an amplifier and a bridge circuit having two pairs of bridge junctions an a second dielectric capacitor included as an arm element thereof, said amplifier operatively supplying its output signal to one pair of the bridge junctions and being supplied with a signal appearing at the other pair of the bridge junctions to form a feed back oscillation circuit therewith, and said dielectric material being commonly utilized in said secondmentioned dielectric capacitor with a close relationship to said first mentioned dielectric capacitor thereby providing a radiofrequency heating on the dielectric material.

3. A signal modulating device as defined in claim 2, wherein said dielectric material is formed in a plate shape and the first and second dielectric capacitors are formed on said plate such that said second capacitor surrounds said first capacitor.

4. A signal modulating device comprising:

a dielectric capacitor utilizing nonlinear dielectric material and exhibiting a nonlinear reactance characteristics in accordance with a change in a signal applied thereto at a constant temperature in the vicinity of the Curie point thereof; 7

a radiofrequency heating device for heating said capacitor to maintain the same at the constant temperature during operations;

input means including a resistor for applying an input signal to said capacitor through said resistor;

a transformer having primary and secondary windings;

means for supplying to said primary winding of the transformer a carrier having a relatively high alternating frequency with respect to said input signal;

means for connecting said secondary winding of the transformer to said capacitor to supply said carrier to the capacitor; and

output means including filter means for selectively obtaining even-harmonics of the carrier modulated by said input signal from an output signal of the capacitor, said resistor being designed to exhibit a relatively low resistance in response to the input signal but a relatively high resistance to the carrier, and said filter means being designed to selectively obtain even-harmonics of the car rier modulated by said input signal from an output signal of the capacitor.

5. A signal modulating device comprising;

a pair of serially connected nonlinear dielectric capacitors exhibiting the same nonlinear reactance characteristics in accordance with change in a signal applied thereto at a constant temperature in the vicinity of the Curie point thereof;

lid

radiofrequency operated heating means for maintaining said nonlinear dielectric capacitors at the constant temperature during operations;

a transformer having a primary winding and a secondary winding with a middle tap;

means for connecting said secondary winding of the transformer to said serially connected capacitors to form a bridge circuit having two pairs of bridge junctions one of which are formed of two junctions between said respective capacitors and said secondary winding of the transformer and the other of which are formed of the junction between the capacitors and of the middle tap of the secondary winding;

input means including an input impedance element for apl plying an input signal between one of the pairs of the bridge junctions through said input impedance element, said input impedance element being designed to exhibit a relatively low impedance in response to the input signal but a relatively high impedance to said carrier; means for applying between the other of the pairs of the bridge junctions a carrier having a relatively high alternating frequency with respect to said input signal; and output means signal selectively obtaining even-harmonics of the carrier modulated by said input signal from nonlinear output characteristics of the bridge circuit appearing between a signal second mentioned junctions applied with the input signal.

:7: t 111! l i pair of the bridge 

1. A signal modulating device comprising: at least one nonlinear reactance element which exhibits nonlinear reactance characteristics in accordance with a change in a signal applied thereto at a constant temperature in the vicinity of the Curie point thereof; heating means for maintaining said nonlinear element at the constant temperature in the vicinity of the Curie point during operation; means for applying to said nonliner reactance element a carrier having a relatively high alternating frequency with respect to said input signal; input means including an input impedance element for applying an input signal to said nonlinear element through said input impedance element said input impedance element being designed to exhibit a relatively low impedance in response to said input signal, but a relatively high impedance in response to said carrier; and output means for selectively obtaining from an output signal of the nonlinear reactance element even-harmonics of the carrier modulated by said input signal.
 2. A signal modulating device as defined in clam 1, wherein said nonlinear reactance element is a dielectric capacitor utilizing dielectric material which exhibits nonlinear characteristics of its dielectric constant in accordance with change in a signal applied thereto, and said heating means comprises an amplifier and a bridge circuit having two pairs of bridge junctions an a second dielectric capacitor included as an arm element thereof, said amplifier operatively supplying its output signal to one pair of the bridge junctions and being supplied with a signal appearing at the other pair of the bridge junctions to form a feed back oscillation circuit therewith, and said dielectric material being commonly utilized in said second-mentioned dielectric capacitor with a close relationship to said first mentioned dielectric capacitor thereby providing a radiofrequency heating on the dielectric material.
 3. A signal modulating device as defined in claim 2, wherein said dielectric material is formed in a plate shape and the first and second dielectric capacitors are formed on said plate such that said second capacitor surrounds said first capacitor.
 4. A signal modulating device comprising: a dielectric capacitor utilizing nonlinear dielectric material and exhibiting a nonlinear reactance characteristics in accordance with a change in a signal applied thereto at a constant temperature in the vicinity of the Curie point thereof; a radiofrequency heating device for heating said capacitor to maintain the same at the constant temperature during operations; input means including a resistor for applying an input signal to said capacitor through said resistor; a transformer having primary and secondary windings; means for supplying to said primary winding of the transformer a carrier having a relatively high alternating frequency with respect to said input signal; means for connecting said secondary winding of the Transformer to said capacitor to supply said carrier to the capacitor; and output means including filter means for selectively obtaining even-harmonics of the carrier modulated by said input signal from an output signal of the capacitor, said resistor being designed to exhibit a relatively low resistance in response to the input signal but a relatively high resistance to the carrier, and said filter means being designed to selectively obtain even-harmonics of the carrier modulated by said input signal from an output signal of the capacitor.
 5. A signal modulating device comprising; a pair of serially connected nonlinear dielectric capacitors exhibiting the same nonlinear reactance characteristics in accordance with change in a signal applied thereto at a constant temperature in the vicinity of the Curie point thereof; radiofrequency operated heating means for maintaining said nonlinear dielectric capacitors at the constant temperature during operations; a transformer having a primary winding and a secondary winding with a middle tap; means for connecting said secondary winding of the transformer to said serially connected capacitors to form a bridge circuit having two pairs of bridge junctions one of which are formed of two junctions between said respective capacitors and said secondary winding of the transformer and the other of which are formed of the junction between the capacitors and of the middle tap of the secondary winding; input means including an input impedance element for applying an input signal between one of the pairs of the bridge junctions through said input impedance element, said input impedance element being designed to exhibit a relatively low impedance in response to the input signal but a relatively high impedance to said carrier; means for applying between the other of the pairs of the bridge junctions a carrier having a relatively high alternating frequency with respect to said input signal; and output means signal selectively obtaining even-harmonics of the carrier modulated by said input signal from nonlinear output characteristics of the bridge circuit appearing between a signal second mentioned pair of the bridge junctions applied with the input signal. 